It is common knowledge that strengthening thermoplastics with fibrous material such as glass fibers produces materials with better mechanical properties. A number of different procedures for accomplishing this end have been described, for example, the method described in U.S. Pat. No. 2,877,501 wherein a thermoplastic granule containing glass fiber oriented along a single direction is described. However, a problem encountered in present methods of preparing fiber containing thermoplastic material in granular or pelleted form for molding operations is that during the production of small pieces of the composite, the fiber is degraded in quality and length and resulting molded articles produced using the pieces show neither the uniform fiber distribution nor mechanical properties shown by molded items produced directly from thermoplastic powder and fibers without the intermediate step of producing molding composite. The intermediate step of producing a molding composite wherein the fiber and thermoplastic material is, for example, pelleted, is desirable as among other things the pellets simplify subsequent molding operations.
Now it has been found that the above problems can be avoided if pellets of thermoplastic material and fiber bundles are produced in a manner which avoids shearing during the mixing of the fiber bundle and thermoplastic material and in a manner which randomizes the fiber bundle orientation substantially in two dimensions prior to fluidization of the thermoplastic material.